Rectilinear potentiometer



1965 D. c. BAKER ETAL RECTILINEAR PQTENTIOMETER 2 Sheets-Sheet 1 Filed Feb. 19. 1962 m m 0 E T A T N A M EBSM V .w m L B 0%.. L A A H N NCA 0 I L D R A By W Jan; 19, 1965 D. c. BAKER ETAL RECTILINEAR POTENTIOMETER 2 Sheets$heet 2 UTILIZATION Filed Feb. 19, 1962 DEVICE Fig. 3

JNVENTORS DONALD C. BAKER RICHARD L.SM|TH ALAN L. BAUMGART By & 164M United States Patent Ofiice Fatented Jan. 1%, 1965 3,166,729 REQTIMNEAR PGTENTIGMETER Donald C. Baker, 44? Pine Needles Drive, Del Mar, Calirb; Richard L. Smith, Natienal City, Guild; and Alan L. llaunigart, 6828 Halifax 8t, San Diego, Qalii; said Smith assiguor to Qaliforuia General, inc, Chula Vista, Calif.

Filed Feb. 19, 1962, Ser. No. 173,876 9 Claims. (Cl. 338-183) This invention relates to an electrical component, and

more particularly to one that falls into the classification of rectilinear otentiometers.

Background It is frequently desirable to adjust an electrical circuit in .a continuous manner, or in very small steps. Some of the most common of such uses are the adjusting of the volume of a radio, and adjusting the tone of a highfidelity sound system. In industry, there are many such applications; and very frequently it is necessary to have very fine adjustments.

One way of achieving this result is to have a long resistance wire, and to slide a contact, or wiper, along the wire. It is evident that a small movement of the wiper will bring it to a position where the resistance is slightly different than it was at the wipers original position. The disadvantage of this method is that for high resistances, the wire length, and therefore the movement of the wiper, is very great.

One improvement uses a resistance wire helically coiled around a mandrel. This improvement has the advantage of shortening the movement of the wiper, but now the wiper jumps from one coil to another. This has two main disadvantages. The first is that the changes are now in steps, rather than being continuous; and secondly, the steps are of a value equal to the resistance of Wire in each coil; and for high valued resistance wire, the resistance per coil, and therefore the steps, are quite large.

Two obvious solutions are (1) to use small coils, and (2) to use wires whose resistance per coil is small.

Unfortunately, each of these solutions postulates a long travel for the wiper.

Another problem arises with components of the above type when it is desired to permanently connect a wire to the resistance wire to form a so-called tap. In the past the resistance wire was tightly wound helical fashion around a mandrel, and it was difficult to separate a single coil of the resistance wire to make the desired connection.

Still another problem arose in the manufacture of a rectilinear component, that is, one wherein the mandrel was straight, the wiper travelling-back and forth in a straight line, and all the external connections were at the same end of the component Since the resistance wire had one end thereof distal from the connection end, it became difficult for the connection to the distal end to be brought out of the structure at the same end as the other Wires, especially in small or miniaturized units.

Objects and drawings of the invention to provide an It is a further object of the invention to provide an electrical component of the resistance-wire type wherein it is practicable to have all the external connections at one end of the components. I

The attainment of these objects and others will be realized from the following specification, taken in conjunction with the drawings, in which:

FIGURE 1 is a perspective view of structure embodying the basic concept of the invention;

FIGURE 2 is a fragmentary View showing how a taplead wire can be connected to a selected point of the resistance wire, and brought out into the open;

FIGURE 3 is a partially diagrammatic top View of a rectilinear potentiometer embodying the inventive con cept of the instant invention; and

FIGURE 4 is an enlarged cross sectional view taken along the line 44- of FIGURE 3.

Brief description of the invention Broadly stated, the instant invention comprises the concept of using two resistance wires that are connected in parallel. These wires are helically wound around a mandrel that comprises two adjacent tubes of insulative material. In winding the helical coils, one wire starts half a turn before the other, so that at any given position of the wiper one wire has half a turn more length than the other wire. The triangularly shaped channel between the tubes permits a single wire to be manipulated for a tapping connection, and the hollow center portion of the tube permits a lead wire connection to the distal end of the resistance wire.

Detailed structure, the inventive concept, the theory, and the explanation of operation will be presented in the following specification.

Detailed description of the invention The basic inventive concept will be understood from FIGURE 1. Here the resistance-Wire unit 10 has a mandrel 11 that comprises two parallel, adjacently positioned glass tubes 12 and 14. Any insulative material may be used, but glass has the advantages that the tubes are moisture-resistant, of uniform diameter, electrically insulative, and of substantially constant dimension throughout their lengths.

As shown, two insulated resistance wires 16 and 18 are helically wound around composite mandrel 11 in an interleaved fashion. Resistance wire 16 starts at the top of tube 12, whereas resistance wire 18 starts at the bottom of tube 14 both being anchored in place, and being electrically connected to a band 28* to which a first lead wire 22 is attached. If desired, the band may serve the dual functions of anchoring the resistance wires in place, and simultaneously connecting them together electrically and serving as a terminal to which lead wire 22 is connected. Alternatively, separate anchoring and connecting means may be used.

in a similar manner, resistance wire 16 terminates at the bottom distal end of mandrel 11, whereas resistance wire 18 terminates at the top distal end of mandrel 11. The terminating ends of resistance wires 16 and 18 are secured in any suitable manner, and a common connection, such as band 24 is connected to the second lead wire 26. Lead wire 26 is then fed through the hollow center of one glass tube, so that it may appear at the near end of unit it If desired, the tube containing the second lead wire 26 may be made longer, so that the second lead wire 26 may be readily anchored to mandrel 11 by means of another band 28. This band may be used merely as an anchor, or alternatively may also be used as an electrical connection for external lead wire 34). Alternatively, the two tubes may be of the same length, band 28 being positioned on an unwound portion thereof.

- terms of half a turn of resistance wire 18. case, this half-turn difference is in parallel with the Wires l6 and is are tightly wound around mandrel ll, and are closely adjacent each other. The adjacent turns are thus pressed tightly against each other, and securely anchored by the action of bands 26) and 2d; but, if desired, a cement may be used to bond the adjacent turns together, and to the mandrel ll.

A wiper 32, shown symbolically, makes electrical contact with two adjacent coilsof resistance wires lid, and l.

Theory of invention Assume, for ease of explanation, that the total resistance of the resistance unit lltl must equal 55 ohms. A single prior-art resistance wire having 55 ohms may be wrapped helically around a single mandrel in five turns, so that as the wiper moves from one turn to the next the resistance changes in units of eleven ohms.

The instant invention uses two wires, lid and 18, each of which has a resistance of 110 ohms; but since their' ends are electrically tied together their effective resistance is half of 110 ohms, or 55 ohms, the desired value.

' Since wires 16 and 18 have twice the resistance of the prior-art resistance wire, their cross sections may be half as large; and their diameters may be only one quarter as large. Thus the two resistance wires in and it? may e closely spaced, and still require a mandrel of substantially the same length as prior-art units.

The uppermost portions of the turns of resistance wires 16 and 1.8 are stripped of insulation, so that electrica contact can be made to each separate turn.

At any given location of wiper 32, it contacts adjacent turns of both wires, 16 and 13. If the wiper were at the mid-point of the wires it would contact cach'wire at substantially its 55 ohm point; and the two parallel-connected wires would thus produce an effective resistance of half 55 ohms, or 27.5 ohms. This is the value that should result from a mid point setting of wiper 32. The above arrangement therefore provides a resistance-wire unit having such small changes of resistance between adjacent positions of the wiper, that the resistance variations are practically of the continuous type.

Moreover, the use of. small-diameter closely-spaced resistance wire, and a wiper that rests on two adjacent turns, permits wiper 32 to glide over the adjacent coils, rather than falling into the spaces between them. This permits a longer useful life, less wear, and a smoother operation and positioning of the wiper.

The interleaved windings of resistance wires 16 and 13, being in a 180 degree out-of-phase relation, provide even smaller steps between adjacent positions of wiper 32 as follows. Since one resistance wire starts at'tthe top of mandrel 11 while the other starts at the bottom of the mandrel, spatially corresponding points of any two adjacent turns of the resistance wires are electrically one half turn apart.

The above situation may be seen from FIGURE 1. It will be evident that when wiper 32 is at the position indicated by the solid line representation, itcontacts a point of wire 18 that is one-half a turn nearer the proximal end than the contacted point of wirello. It will also be evident that when Wiper 32 is at the dotted line position, it contacts a point of wire 13 that is one-half a turn farther from the proximal end than the contacted point of wire 16, which is the same in each case.

Thus, adjacent positions of wiper 32 are therefore in Since, in each value of resistance wire 16 for that setting of the wiper, the changeof effective resistance is closer to the Value for one-quarter turn of resistance wire.

The foregoing discussion has implied that the exact ends of the resistance wires 16 and 18 are connected together, and that one helix starts at thetop of the mandrel while the other starts at the bottom. A similar implication has existed for the terminatingends of the helixes.

will be obvious that it bands 2t and 24 are conductive, they will contact the separate helixes at substan tially diametrically spaced points; thus producing .the-

same effect as the helixes started and terminated at the tops and bottoms of the mandrel. Similarly, conductive bands such as 2t? and-Z4 may be positioned inwardly from the actual ends of the resistance wires; but to all eilects they establish the electrical ends thereof by means of the connections of the lead wires. The term end of wire and the like should therefore be construed in terms of the above discussion.

it was previously indicated that the instant invention permitted easier connecting to particular portions of the resistancewire, as required for permanently positioned tap connections.

In prior art devices of this type, the resistance wire was tightly Wound around the mandrel, and even ceed to it, to prevent movement of the resistance wire as thcwiper moved from coil to coil. when a lead wire was to be attached to a given coil, that point of the coil had to be forcibly pulled away from the mandrel in order to make the connection. This was difficult, because a hook or sharp-pointed instrument had to be forced between the mandrel and the coil of the resistance wire, without injuring the insulation of any wires, and without kinking any of the Wires.

The ease of providing a tap connection in the instant invention is shown in FIGURE 2. As shown, the various coils of wire 16, it; span the triangular channel between elcmcnts I12 and M of themandrel; and they are e; re spaced from, and not cemented to the mandrel -r. it is therefore relatively easy to insert a hooked pi instrument, such as 34, under one or two wires as desired, and to separate the selected wire from the other coils. A lead wire such as 36 may be electrically connected to the chosen wire, and brought out through the triangular channel.

in this way a tapped connection is tap lead wire does not interfere with the operation of the wiper; and the tap lead wire can also be brought out to the same end as other lead wires.

FIGURE 3 showsthe instant invention incorporated into a rectilinear potentiometer. The electrical component 38 contains the previously described resistance-wire unit in and its associated lead wires 22 and 3%, these lead wires being connected to the opposite terminals of a potential source T to wiper 32 is moved by means of a shaped wiper block 42 that slides along a complementary shaped channel, and is in turn fastened to the end of a slidable rod 44.

easily made; the

Wiper 32 may take any suitable form, the illustration showing it asa rectangularly bent strip of wire having its central portion embedded in a conformingslot of the wiper block d2. The end portions of the wiper 32 are therefore resiliently positioned; one end moving along resistance-wire unit in as previously described, while the other end moves along a conductive bar 46 whose lead wire 48 is connected to a utilization device 55).

The working mechanism of component 33 is preferably enclosed in a housing 52 that is substantially sealed to provide a relatively moisture-proof and dust-proof environment.

In FIGURE 4- there is shown a cross sectionalview to illustrate the relative positions of the internal parts of unit 38. I Resistance-wire unit ltl and conductive bar 46 as mounted along the edges or" a semi-cylindrical guide member 54 that has a modified U-shaped elongate slot. The slot thus forms a channel 5: having a cross section that is complementary to that of wiper block 42, and along which wiper block 42 moves. Slidable actuating rod 44- may be attached to wiper block in any convenient manner, but we it particularly convenient to use a hairpin spring that tits through a slot of the wiper block, and snaps into an annular 'groove '57 of the slidable rod, the. rod being freely rotatable.

This meant that i Operation of the invention The instant invention is preferably used as a potentiometer, since in this way the contact between the wiper and the resistance wire carries practically no current, and thus obviates arcing and erosion of the wiper and/or the resistance wires.

In this mode of usage, the ends of the resistance wires are connected across a source of potential, as illustrated in FIGURE 3. Since the potential source and the resistance of the wires remains substantially constant, a fixed current flows through the resistance wires, so that the voltage drop along their length remains constant.

The wiper 32 contacts two selected coils of the resistance-unit 10, and the potential at this point is transmitted over conductive bar 46, and lead wire 48 to utilization device 59. This device may be a load, a measuring device, an amplifier, or the like; and should have a high input impedance so that it does not draw current from the resistance unit as previously suggested.

As actuating bar 44 is moved longitudinally, it causes wiper block 42 to slide along its channel, and thus reposition wiper 32. The relation between the wiper block and its channel causes the block to have a straight line, or rectilinear movement, which assures that the ends of the wiper move smoothly along their given paths with substantially constant pressure.

The disclosed method of attaching the slidable bar 44 to the wiper block 42 permits the bar to rotate without placing any stress, strain, or torque on the wiper block. In addition, slidable bar 44 is supported by the block and by the opening through housing 52, so there is no tendency to bend the bar.

As the bar slides back and forth, it-positions the wiper,'

which applies corresponding a potential to utilization device 50. Thus if the end of bar 44 is positioned against a surfiace 58, and the end of housing 52, or a fixed length bar 60 attached thereto, is positioned against another surface 62, the position of wiper 32 will correspond to the distance between surfaces 58' and 62. Due to the extremely fine resolution or" the device, it may thus be used as an electrical micrometer, using only a battery and a fairly sensitive voltmeter. A spring 64 may be fitted on rod 44 to bias the rod outwardly and facilitate measuring. To provide a small sliding friction and prevent inadvertent displacement of the wiper block 42, a leaf spring 66 may be fitted between said block and the bottom of channel 55.

The instant invention may also be used as a sensitive, high-resolution potentiometer; the uses of which are well known.

It should also be noted that the use of two adjacent tubes permits the lead wires to be grouped at the same end of the unit; this feature being of great importance when the unit is mounted in such a manner that only one end thereof is available for connections and the like.

A dvantages It will be evident thatour invention has numerous advantages over prior-art devices. Firstly, it is truly rectilinear, and remains so after long usage due to the matched shapes of the wiper block and the channel, and the alignment of the end wall opening that is traversed by the slidable rod. Secondly, the adjacently positioned mandrel rods facilitates connection to selected wires, and the feeding of the tap lead wire. Thirdly, the use of tubularelements for the mandrel permits the connection to the distal end of the resistance wire to be brought out at the same end as the other wires. Fourthly, the hairpin spring method of attaching the slidable bar to the wiper block obviates the danger of twisting the block. And finally, the 180 degree out-of-phase winding of two resistance wires produces a one-half turn difference in wiper position, thus providing a device with extremely small steps between adjacent positions of the wiper.

greater It is understood that minor variation from the form of the invention disclosed herein may be made without departure from the spirit and scope of the invention, and that the specification and drawing are to be considered as merely illustrative rather than limiting.

We claim:

1. The combination comprising:

an elongated guide member having a substantially U-shaped elongated longitudinal slot;

an elongate conductive bar positioned along the top ofone side of said guide member;

an elongate resistance-wire unit positioned along the top of said other side of said guide member;

a wiper block slidably positioned in said U-shaped slot for longitudinal movement therein said block being of complementary shape compared to said slot;

a wiper mounted on said block, said wiper having one end in slidable contact with said bar, and having the other end in slidable contact with said resistance wire unit;

an actuating rod having one end attached to said block, said attachment comprising a hairpin-type spring, whereby said rod may rotate freely with respect to said block without applying any torque thereto, but may move said block slidably along said slot.

2. The combination of claim 1 wherein said resistancewire unit comprises two shunt-connected resistance wires wound in a degree out-of-phasc helical manner.

3. The combination of claim 1 wherein said resistancewire unit comprises a resistance wire helically wound around an elongate mandrel having a longitudinal passageway therethrough; and a lead wire connected to the distal end of said resistance wire, said lead wire traversing said passageway and exiting at the other end thereof.

4. The combination of claim 1 wherein said resistance wire unit comprises a pair of parallel-connected resistance wires helically wound around two parallel contiguously positioned elongated elements, at least one of said elements having a longitudinal passageway therethrough; means for electrically connecting adjacent ends of said resistance wires; and a lead wire connected to the distal ends of said resistance wires, said lead wire traversing said passageway and exiting at the other end thereof.

5. A potentiometer comprising:

(A) a guide member having a longitudinal slot;

(B) a conductive bar positioned along the top of one side of said guide member;

(C) a first lead wire connected to said conductive bar and exiting adjacent the proximal end thereof;

(D) a resistance-wire unit positioned along the top of said other side of said guide member, said unit comprising:

( 1) two parallel positioned glass tubes,

(2) a pair of resistance wires helically wound around said tubes in a 180 degree out-of-phase manner,

(3) means for electrically connecting the adjacent ends of said resistance wire;

(4) a second lead wire connected to the distal ends of said resistance wires, said second lead wire traversing the center of one of said glass tubes and exiting at the proximal end thereof;

(5) a third lead wire connected to the proximal ends of said resistance wires, and exiting adja cent said proximal end;

(E) a wiper block slidably positioned in said slot for longitudinal movement therein;

(F) a wiper mounted on said block, said wiper having one end in slidable contact with said bar, and having the other end in slidable contact with said resistance wire unit; and

(G) an actuating rod having one end attached to said block, whereby said rod may move said block slidably along said slot.

6. A potentiometer comprising:

(A) an elongated guide member having a substantially U-shaped elongated longitudinal slot;

(B) an elongated conductive bar positioned in a recess along the top of one side of said guide member; (C) a first lead wire connected to said conductive bar and exiting adjacent the proximal end thereof;

(D) an elongate resistance-wire unit positioned in a recess along the top of said other side of said guide member, said unit comprising:

(1) two parallel contiguously positioned glass tubes,

(2) a pair of equi-valued resistance wires helically wound around said tubes in a 180 degree out-ofphase manner,

(3) means for electrically connecting the adjacent ends of said resistance wires:

(4) a second lead wire connected tothe distal ends of said resistance wires, said second lead wire traversing the center of one of said glass tubes and exiting at the proximal end thereof;

(5) a third lead wire connected to'the proximal vends of said resistance wires, and exiting adjacent said proximal end;

(E) a Wiper block slidably positioned in said U-shaped slotfor longitudinal movement therein, said block being of complementary shape compared .to said slot;

(F) a wiper mounted on said block, said wiper having one end in slidable contact with said bar, and having the other end in slidable contact with said resistance wire unit, the potential picked up by said wiper appearing at said first lead wire;

(G) an actuating rod having one end attached to said block, said attachment comprising a hairpin-type spring, whereby said rod may rotate freely with respect to said block without applying any torque thereto, but may move said block slidably along said slot; and

8 i (H) a housing enclosing elements A-G, all said lead wires traversing said housing at the same end thereof. 7. The combination of claim 6 wherein said actuating rod traverses said housing at the end thereof opposite 5 said lead wires.

8. The combination comprising:

a composite mandrel comprising a pair of rod-like elongated elements positioned in a parallel closely-adjacent manner;

a wire helically Wound around said mandrel, whereby said wire spans the triangularly spaced area between said elements; and I a tap lead wire positioned in said area, said lead wire being connected to a portion of said wire spanning said area.

9. The combination comprising:

a composite mandrel comprising i a pair of rod-like elongated elements positioned in a parallel closely-adjacent manner, at least one of said elements having a longitudinal passage therethrough;

a resistance wire helically wound around said mandrel, whereby said wire bridges the triangularly spaced area between said elements;

a tap lead wire positioned in said area, said lead wire being connected to a portion of said resistance wire spanning said area; and

means for connecting a second lead wire to the distal end of said resistance wire, said second lead wire passing through said passageway to exit adjacent the proximal end of said passageway.

References Cited in the file of this patent UNITED STATES PATENTS 

1. THE COMBINATION COMPRISING: AN ELONGATED GUIDE MEMBER HAVING A SUBSTANTIALLY U-SHAPED ELONGATED LONGITUDINAL SLOT; AN ELONGATE CONDUCTIVE BAR POSITIONED ALONG THE TOP OF ONE SIDE OF SAID GUIDE MEMBER; AN ELONGATE RESISTANCE-WIRE UNIT POSITIONED ALONG THE TOP OF SAID OTHER SIDE OF SAID GUIDE MEMBER; A WIPER BLOCK SLIDABLY POSITIONED IN SAID U-SHAPED SLOT FOR LONGITUDINAL MOVEMENT THEREIN SAID BLOCK BEING OF COMPLEMENTARY SHAPE COMPARED TO AID SLOT; A WIPER MOUNTED ON SAID BLOCK, SAID WIPER HAVING ONE END IN SLIDABLE CONTACT WITH SAID BAR, AND HAVING T HE OTHER END IN SLIDABLE CONTACT WITH SAID RESITANCE WIRE UNIT; AN ACTUATING ROD HAVING ONE END ATTACHED TO SAID BLOCK, SAID ATTACHMENT COMPRISING A HAIRPIN-TYPE SPRING, WHEREBY SAID ROD MAY ROTATE FREELY WITH RESPECT TO SAID BLOCK WITHOUT APPLYING ANY TORQUE THERETO, BUT MAY MOVE SAID BLOCK SLIDABLY ALONG SAID SLOT. 